Absorbent products such as industrial wipers, food service wipers, and other similar items are designed to combine several important attributes. For example, the products should have good bulk, a soft feel and should be highly absorbent. The products should also have good strength even when wet and should resist tearing. Further, the wiping products should have good stretch characteristics and should not deteriorate in the environment in which they are used.
In the past, many attempts have been made to enhance and increase certain physical properties of wiping products. Unfortunately, however, when steps are usually taken to increase one property of a wiping product, other characteristics of the product may be adversely affected. For instance, in some wiping products, strength can be increased by embossing the web to thermally bond fibers contained therein. However, in certain instances, such thermal bonding can result in a web that contains substantial areas of melted polymer. Typically, these areas have a decreased functionality, i.e., absorption capacity, bulk, etc.
As such, a need currently exists for a method for bonding a wiping product such that it can have improved functionality and also remain relatively strong.
The present invention is generally directed to fabrics formed from nonwoven webs that are bonded by microcreping. In particular, it has been discovered that the frictional forces associated with microcreping can cause the fibers within a web to bond together to provide web strength. Moreover, it has also been discovered that microcreping does not generally result in a web having substantial areas of melted polymer such that the web can have improved functionality, i.e., absorption capacity, bulk, etc.
Nonwoven webs used in the present invention can generally be formed from any of a variety of materials, such as various materials commonly used in the art for making wipers. In particular, a nonwoven web of the present invention is typically made from synthetic fibers, pulp fibers, thermomechanical pulp, or mixtures thereof. For instance, in one embodiment, the nonwoven web can be made exclusively from polyolefin fibers. In another embodiment, the nonwoven web can be made from polyolefin fibers and pulp fibers. When utilizing synthetic fibers, such as polyolefin fibers, in conjunction with pulp fibers, the synthetic fibers can generally be added to the web in any desired amount. For example, in one embodiment, polyolefin fibers are added in an amount of at least about 20% by weight of the web, particularly at least about 40% by weight of the web, and more particularly at least about 60% by weight of the web.
In one particular embodiment, the nonwoven web of the present invention is formed from melt-spun fibers. For example, in one embodiment, the nonwoven web is formed by meltblowing polyolefins or other melt-spinnable fibers into a web formation. In another embodiment, a coform web can be formed by combining melt-spun fibers with pulp fibers, staple fibers, etc., during a meltblowing or spunbonding process. Moreover, if desired, a multi-layered nonwoven web can be formed that contains a first layer formed from a meltblown, spunbond, or coform material and a second layer formed from any other material. For instance, the second layer can be formed from a meltblown, spunbond, coform, or bonded carded material.
In accordance with the present invention, after forming the fibers into a web, the web can then be bonded to improve the strength of the web. In particular, a nonwoven web of the present invention is bonded by microcreping, which is a mechanical compaction process normally used in the art to soften a web. It has also been discovered that microcreping can provide increased bulk and absorbent capacity, while also imparting sufficient strength to the web so that it may be used as a wiper. In one embodiment, for instance, the nonwoven web can be transferred to a treatment zone for microcreping one or both sides of the web. One or more blades may then be utilized to compact the web along at least one of its planar dimensions. For example, in one embodiment, the web can first pass under a primary blade that compresses it in the -z plane (i.e., the plane generally perpendicular to the plane formed by the machine direction and cross-machine direction. As the web passes under the primary blade, it can also contact one or more blades that compress the web in a lengthwise direction. Suitable microcreping equipment may be obtained, for example, from Micrex Corporation of Walpole, Mass.
In general, the extent of microcreping can vary as desired. In particular, by increasing the degree of microcreping, the bulk of the nonwoven web can be increased. However, it is typically desired to control the extent of microcreping so that the strength of the web is also not substantially reduced. For example, in some embodiments, the microcreped nonwoven web can have an extensibility in the lengthwise direction of less than about 30%, and particularly between about 5% to about 25%.
As a result of being bonded by microcreping, the bulk of a nonwoven web of the present invention can generally be increased due to micro-fold formation. Moreover, microcreping can also allow the nonwoven web to have improved absorbency characteristics over nonwoven webs bonded solely by other methods.
Other features and aspects of the present invention are discussed in greater detail below.